A simple method of short‐term mechanical reliability prediction for ceramics in reactive environments

A method is demonstrated for prediction of ceramic reliability limited by fracture in reactive environments. The simplicity of the method relies on the ceramic displaying ideal indentation‐strength behavior and on the applied loading leading to short‐term power‐law crack velocity behavior. Reactive failure strength measurements, treating flaw size as a variable and failure time as a constraint in a “pass‐fail” test, enable reliability, including both intrinsic and contact flaws, to be predicted. Little to no computation is required.     

An environmentally friendly clay‐based polymer composite “paper”

The paper industry is closely related to our daily life. Vast quantities of paper requirement worldwide lead to astonishing lumber consumption and environmental pollution. So the exploration of alternative paper‐like material should be of great importance. Here, we reported the preparation of a kind of environmentally friendly clay‐based polymer composite paper‐like film by incorporation of a kind of nanometer sized natural clay crystals, in this case attapulgite (ATP), into degradable poly(vinyl alcohol) (PVA) only though a simple blending and subsequently casting method. X‐ray analysis shows that no changes in the crystalline structure of ATP were observed in the PVA matrix. Even with a high content of clay crystals in composites (50 wt %), the resulting ATP‐PVA composite films (named as APCF) show excellent flexibility and tensile strength up to 22.19 MPa. The doping of ATP also results in flame retardant of composites, making it ideal candidate for packing and also building decoration applications. Interestingly, the APCF are printable and also much tough and tensile. Due to the simple fabrication, nearly no pollution emission process and easily to be scaled up, the APCF have great potentials as a kind of alternative for paper materials for diverse applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45128.     

Thermal‐cycle dependent residual stress within the crack‐susceptible zone in thermal barrier coating system

Nondestructive and accurate measurement of residual stress in ceramic coatings is challenging, but it is crucial to the assessment of coatings failure and life. In this study, for the first time, the thermal‐cycle dependent residual stress in an atmosphere plasma sprayed thermal barrier coating system has been nondestructively and accurately measured using photoluminescence piezo‐spectroscopy. Each thermal cycle consists of a 5‐minute heating held at 1150°C and a 3‐minute water quenching. The measurement was performed within a crack‐susceptible zone in the yttria‐stabilized‐zirconia (YSZ) top coat (TC) closely above the thermally grown oxide layer. A YSZ:Eu³⁺ sublayer was embedded in TC as a stress sensor. It was found that the initial residual stress was compressive, with a mean value of 240 MPa, which rapidly increased to 395 MPa after 5 thermal cycles (12.5% life) and then increased gradually to the peak of 473 MPa after 25 thermal cycles (62.5% life). After 30 thermal cycles (75% life), the mean stress dropped abruptly to 310 MPa and became highly heterogeneous, with gradual reduction toward final spallation. The heterogeneous stress distribution indicates that many microcracks nucleated at different locations and the spallation occurred due to the coalescence of the microcracks.     

Eggshell reinforced biocomposite—An advanced “green” alternative structural material

The need for bio‐based polymers as substitutes to recalcitrant petroleum sourced plastics is ever growing, because of increase in demand globally. Eggshell nanopowder (ENP) prepared using mechanical attrition and ultrasound irradiation was used to infuse a bio‐based polymer [Super Sap 100/1000 epoxy (SSE)] for possible enhancement of its mechanical properties. The ENP, neat SSE and SSE/ENP composites were characterized using X‐ray Diffraction, Transmission Electron Microscopy (TEM), Energy dispersive spectroscopy (EDS), Scanning Electron Microscopy, Thermogravimetic Analysis (TGA), Dynamic Mechanical Analysis (DMA), Thermomechanical Analysis (TMA) and flexure analysis. TEM and EDS analysis showed evidence of ENP in the SSE matrix whiles DMA and TMA analysis revealed significant improvements (7–22%) in the storage moduli and (3–17%) in coefficient of thermal expansion (CTE) respectively. Also, major delay in 5% decomposition temperatures and increases in char yields were observed in TGA analysis. The flexure strength, modulus, and toughness significantly improved by 6–31%, 11–37%, and 10–36%, respectively. Microstructure of fractured surfaces showed deflected crack paths which contributed to improve toughness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43124.     

Reply to Comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric‐Dielectric System”

In the comment on “The Impact of Composite Effect on Dielectric Constant and Tunability in Ferroelectric–Dielectric System”, Padurariu et al. proposed that a 2D system and a 3D system are not exactly similar: with the increase in dielectric content, the tunability of 2D system increases first and the tunability of 3D system decreases gradually. However, in my recent work, an abnormal increase in tunability was observed in the simulation result of 3D ferroelectric–dielectric model: with the increase in dielectric content from 0 to 60 vol%, the tunability increased from 22.8% to 31.4%.     

In vitro hydrolysis and magnesium release of poly(d,l‐lactide‐co‐glycolide)‐based composites containing bioresorbable glasses and magnesium hydroxide

Magnesium is important for both bone growth and cartilage formation. However, the postoperative intake of antibiotics such as quinolones may cause a reduction in magnesium levels in tissue. The addition of magnesium to scaffolds may therefore be beneficial for the regeneration of osteochondral defects. In this study, porous composite scaffolds were produced by gas foaming of poly(d ,l ‐lactide‐co‐glycolide) (PLGA) rods with magnesium‐containing bioresorbable glasses and magnesium hydroxide as fillers. The in vitro hydrolytical degradation of the composite scaffolds in Tris buffer was followed over a 10‐week period. Mg²⁺ was released in a controlled manner from the scaffolds with varying release profiles between the different materials. Higher glass content resulted in a reduced mass loss compared to scaffolds with lower glass content. As a result of the foaming method, the scaffolds shrank initially, without evidence that the addition of hydrophilic fillers would decrease the initial shrinkage. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42646.     

Salt‐Controlled Selectivity in “on Water” and “in Water” Passerini‐Type Multicomponent Reactions

We have demonstrated that simple sodium salts can completely reverse the product ratios of the Passerini reaction in aqueous media. Furthermore, the use of the “salting‐in” salt and a small excess of the nucleophile gives significantly higher yields than the use of the saturated solution of the nucleophile alone.     

Interrogation of “surface,” “skin,” and “core” orientation in thermotropic liquid‐crystalline copolyester moldings by near‐edge X‐ray absorption fine structure and wide‐angle X‐ray scattering

Injection molding thermotropic liquid‐crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. “Skin‐core” morphologies are often observed in TLCP moldings. Given that both “core” and “skin” orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two‐dimensional wide‐angle X‐ray scattering (WAXS) in transmission and near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4′‐dihydroxy‐α‐methylstilbene (DHαMS)‐based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on‐ and off‐ axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of two D‐π‐A polymers π‐bridged by different blocks and investigation of their photovoltaic property

The synthesis, characterization, photophysical and photovoltaic properties of two 5,6‐bis(octyloxy)benzo[c][1,2,5]thiadiazole‐containing wide‐band‐gap donor and acceptor D‐π‐A alternating conjugated polymers (HSD‐a and HSD‐b) have been reported. These two polymers absorb in the range of 300–700 nm with a band gap of about 1.88 and 1.97 eV. The HOMO energy levels were ?5.44 eV for HSD‐a and ?5.63 eV for HSD‐b. Polymer solar cells with HSD‐b :PC₇₁BM as the active layer demonstrated a power conversion efficiency (PCE) of 2.59% with a high V_oc of 0.93 V, a J_sc of 7.3 mA/cm², and a comparable fill factor (FF) of 0.38 under simulated solar illumination of AM 1.5G (100 mW/cm²) without annealing. In addition, HSD‐a :PC₇₁BM blend‐based solar cells exhibit a PCE of 2.15% with a comparable V_oc of 0.64 V, J_sc of 8.75 mA/cm^?2, and FF of 0.40. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41587.     

Bio‐inspired “green” nanocomposite using hydroxyapatite synthesized from eggshell waste and soy protein

Eco‐friendly and inexpensive “ green” nanocomposites with enhanced functional performances were developed by combining nanoscale hydroxyapatite (HA) synthesized from eggshell waste (nEHA) and protein‐based polymer extracted from defatted soybean residues. nEHA was synthesized from chicken eggshells using an energy efficient microwave‐assisted wet chemical precipitation method. Transmission electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy studies confirmed the nanometer scale (diameter: 4–14 nm and length: 5–100 nm) of calcium‐deficient (Ca/P ratio ～1.53) needle‐like HA. Uniform dispersion of nEHA in soy protein isolate (SPI) solution was obtained by modifying nEHA surface using a polyelectrolyte (sodium polyacrylate) dispersant via irreversible adsorption. Green nanocomposite films were prepared from SPI and surface‐modified nEHA with the help of a natural plasticizer “glycerol” by solution casting. Significant improvements in tensile modulus and strength were achieved owing to the inclusion of uniformly dispersed nEHA in SPI sheets. Overall, this work provides a green pathway of fabricating nanocomposites using naturally occurring renewable polymer and inorganic moieties from eggshell waste that emphasizes the possibilities for replacing some petroleum‐based polymers in packaging and other applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43477.     

Semiaromatic polyamide poly(hexamethylene terephthalamide)‐co‐polycaprolactam: Thermal and flame‐retardant properties

The poly(hexamethylene terephthalamide)‐co‐polycaprolactam (PA6T/6; 50:50) copolymer was synthesized with a reactive extrusion method and subsequently mixed with a certain content of glass fibers (GFs) and different ratios of flame‐retardant aluminum diethyl phosphinate (AlPi) to fabricate a series of composites. These resulting composites were found to have excellent mechanical (tensile strength = 119–154 MPa) and thermal properties (heat‐deflection temperature = 263–293 °C). It is particularly worth mentioning that the value of the limiting oxygen index reached 29.5% and a UL‐94 V‐0 rating (1.6 mm) was achieved with the addition of 20 portions of AlPi. Also, the values of the peak heat‐release rate and total heat release in cone calorimetry were found to decrease with the addition of the flame‐retardant AlPi, which acted mainly as a flame inhibitor in the gas phase. Through visual observation, scanning electron microscopy after cone calorimetry testing, and thermogravimetric analysis, the condensed‐phase flame‐retardant mechanism of the PA6T/6–GF–AlPi system was confirmed to have a synergetic role. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46451.     

Development of a Continuous Segmented Flow Tubular Reactor and the “Scale‐out” Concept – In Search of Perfect Powders

The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production.     

Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. II. The “vertical‐shift” mode and intrinsic “time–strain clock”

As in part I of this study, in the same manner in the present part II as well, by the same modus operandi way, an attempt was made to introduce, by means of a given operational mode, some further practical parameters for a “by‐eye” but well‐proven experimental viscoelastic characterization of a polymeric solid. Thus, through consideration of the peculiar vertical shift behavior of the apparent modulus (?) of isotactic polypropylene (iPP) and based on the KWW model, it is shown that, in an empirical and a formalistic sense, a relevant effective or equivalent (single) characteristic relaxation time can be introduced which can give some new interpretations for the linear and nonlinear viscoelastic behavior of a polymeric material, as that of a “time–strain clock,” which, as an intrinsic function, is responsable for a functional time–strain shift of the relaxation time and, at the same time, for a shift toward to a more linear or to a more nonlinear behavior. In the above context of attempts, another functional relationship was shown, the so‐called spectral shift function and its corresponding parameter of nonlinearity strength, through which some further interpretations and characterizations connected with the existence of the permanent internal stress could be made. Finally, the introduction of the so‐called spectral isostrains and their corresponding “spectral inversion point” complete the “set” of the operative parameters proposed for the above‐mentioned purpose. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 138–148, 2003     

The use of poly (ε‐caprolactone) to enhance the mechanical strength of porous Si‐substituted carbonate apatite

Poly(ε‐caprolactone) (PCL)/silicon‐substituted carbonate apatite (Si‐CO3Ap) composite derived from the interconnected porous Si‐CO3Ap reinforced with molten PCL was prepared. PCL was used to improve the mechanical properties of a porous apatite by a simple polymer infiltration method, in which the molten PCL was deposited through the interconnected channel of porous Si‐CO3Ap. The PCL covered and penetrated into the pores of the Si‐CO3Ap to form an excellent physical interaction with Si‐CO3Ap leading to a significant increase in diametral tensile strength from 0.23 MPa to a maximum of 2.04 MPa. The Si‐CO3Ap/PCL composite has a porosity of about 50–60% and an interconnected porous structure, with pore sizes of 50–150 μm which are necessary for bone tissue formation. These results could pave the way for producing a porous, structured biocomposite which could be used for bone replacement. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Crystallization behavior of “wet brush” and “dry brush” blends of PS‐b‐PEO‐b‐PS/h‐PEO

The crystallization behavior of the blending system consists of homopolymer poly(ethylene oxide) (h‐PEO) with different molecular weights, and polystyrene‐block‐poly (ethylene oxide)‐block‐polystyrene (PS‐b‐PEO‐b‐PS) triblock copolymer has been investigated by DSC measurements. The crystallization of PEO block (b‐PEO) in block copolymer occurs under much lower temperature than that of the h‐PEO in the bulk (ΔT > 65 °C), which is attributed to the homogeneous nucleation crystallization behavior of the b‐PEO microdomains. In both the “dry‐brush” and the “wet brush” blending systems, the homogeneous nucleation crystallization temperature of PS‐b‐PEO‐b‐PS/h‐PEO blends increases due to the increase of the domain size. The heterogeneous nucleation crystallization temperatures of h‐PEO in the wet brush blending systems are higher than that of the corresponding h‐PEO in the bulk. At the same time, the heterogeneous nucleation crystallization temperature of b‐PEO10000 decreases from 43°C to 30°C and 40°C in the h‐PEO600 and h‐PEO2000 blending systems, respectively, because of the stretching of the PEO chains in the wet brush. However, this kind of phenomenon does not happen in the dry brush blending systems. The self‐seeding procedure was used to further ascertain the nucleation mechanism in the crystallization process. As a result, the self‐seeding domains have been confirmed, and the difference between the dry brush and wet brush systems has been observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

On the coupled ferroelectric‐electrochromic effect of ε‐WO3

A reversible electrochromic effect has been observed for the first time in flame spray pyrolysis (FSP) processed ε‐WO₃ thin films without the use of an ion storage layer and an electrolytic layer. The dark coloration that appears upon the application of a voltage in films deposited on top of interdigitated gold electrodes is localized to the low voltage (?) electrode arm and it switches to the opposite arm upon a reversal of the polarity. Raman spectroscopy indicated that the coloration was not due to intercalation. It is argued here that the coloration is driven by the asymmetric ferroelectric properties of the ε‐WO₃ crystals and that this electrochromic reversibility is intrinsically coupled with the polarization switching of the device.     

“One‐pot” synthesis of well‐defined functional copolymer and its application as tumor‐targeting nanocarrier in drug delivery

A one‐pot synthesis is developed for PEG₆₀₀‐b‐poly(glycerol monoacrylate) (PEG₆₀₀‐b‐PGA), by which folate and superparamagnetic iron oxide nanoparticles (SPIONs) are assembled to form folic acid‐conjugated magnetic nanoparticles (FA‐MNPs) as a tumor targeting system. The synthesis consists of a “click” reaction and atom transfer radical polymerization (ATRP) to obtain the well‐defined furan‐protected maleimido‐terminated PEG₆₀₀‐b‐poly(solketal acrylate) (PEG₆₀₀‐b‐PSA) copolymer. After deprotection, the key copolymer N‐maleimido‐terminated PEG₆₀₀‐b‐PGA is successfully conjugated with thiol derivatives of folate and FITC, respectively. FA‐MNPs are developed by assembling of the resulting polymer FA‐PEG₆₀₀‐b‐PGA with SPIONs, and characterized for their size, surface charge, and superparamagnetic properties. To investigate the cellular uptake of the nanoparticles by Hela cells and φ2 cells using fluoresce technique, FA‐FITC‐MNPs are also obtained by assembling of FA‐PEG₆₀₀‐b‐PGA, FITC‐PEG₆₀₀‐b‐PGA with SPIONs. Qualitative and quantitative determinations of FA‐FITC‐MNPs show that the particles specifically internalized to Hela cells. No significant cytotoxicity is observed for these two kinds of cell lines. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40405.     

Fabrication and properties of surface‐modified β‐Si3N4 whiskers reinforced dental resin composites

In this article, three kinds of surface‐modified methods were used to treat β‐Si₃N₄ whiskers before being incorporated into Bis‐GMA/TEGDMA dental resin matrix in order to improve the whiskers' reinforcing effect. The experimental results showed that composites with directly heat‐treated and then silanized β‐Si₃N₄ whiskers had the best reinforcing effect. They had flexural strength of 160 ± 7.0 MPa (mean ± SD; n = 6), compressive strength of 371 ± 1.4 MPa (mean ± SD; n = 5) and HRA of 48.4 ± 0.5(mean ± SD; n = 5), respectively. In addition, water sorption and solubility test demonstrated that the composites were reliable to use as the dental restoration materials. Therefore, the directly heat‐treated and then silanized β‐Si₃N₄ whiskers (better than β‐Si₃N₄ whiskers mixed with SiO₂ nanoparticles or SiO₂ sols) were most suitable fillers to reinforce dental resin composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Application of time–stress superposition to viscoelastic behavior of polyamide 6,6 fiber and its “true” elastic modulus

The viscoelastic behavior of semi‐crystalline polyamide 6,6 fiber is exploited in viscoelastically prestressed polymeric matrix composites. To understand better the underlying prestress mechanisms, strain–time performance of the fiber material is investigated in this work, under high creep stress values (330–665 MPa). A latch‐based Weibull model enables prediction of the “true” elastic modulus through instantaneous deformation from the creep‐recovery data, giving 4.6 ± 0.4 GPa. The fiber shows approximate linear viscoelastic characteristics, so that the time–stress superposition principle (TSSP) can be implemented, with a linear relationship between the stress shift factor and applied stress. The resulting master creep curve enables creep behavior at 330 MPa to be predicted over a large timescale, thus creep at 590 MPa for 24 h would be equivalent to a 330 MPa creep stress for ～5200 years. Similarly, the TSSP is applied to the resulting recovery data, to obtain a master recovery curve. This is equivalent to load removal in the master creep curve, in which the yarns would have been subjected to 330 MPa creep stress for ～4.56 × 10⁷ h. Since our work involves high stress values, the findings may be of interest to those involved with long‐term load‐bearing applications using polyamide materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44971.